Optical temperature sensing characteristics of Yb³⁺/Nd³⁺ co-doped YAG single crystal fiber based on up-conversion luminescence

YAG: 5 mol%Yb3+/x mol%Nd3+(x = 0, 0.5, 1, 2, 4, 7) and YAG: 2 mol%Nd3+ single crystal (SC) fluorescent materials were prepared using laser heated pedestal growth (LHPG) method. The up-conversion (UC) spectra of YAG: Yb3+/Nd3+ were recorded under 980 nm laser excitation, the results show that the optimal material was obtained at 5 mol%Yb3+/2 mol%Nd3+. An integrated YAG single crystal fiber (SCF) with end 5 mol%Yb3+/2 mol %Nd3+ co-doped was prepared by the LHPG method, the temperature-dependent characteristics were measured in the range from 348 K to 1448 K. It shows that the fluorescence intensity increases and then decreases with the increase of temperature. Fluorescence intensity ratios (FIR) in Nd3+ UC spectra, including FIR1 (4F7/2/4F5/2 -> 4I9/2), FIR2 (4F9/2/4F5/2 -> 4I9/2) and FIR3 (4G5/2/4F9/2 -> 4I9/2), vary monotonically in temperature ranges of 348-1273 K, 523-1273 K, and 673-1273 K, respectively. The maximally absolute and relative sensitivities for FIR1 were, respectively, achieved to be 2.34 x 10-3 K-1 at 738 K and 4.61 x 10-1 %K-1 at 390 K, and these values for FIR2 were accordingly achieved to be 1.19 x 10-3 K-1 at 1273 K and 4.59 x 10-1 %K-1 at 735 K, and for FIR3 they were 4.66 x 10-3 K-1 at 1273 K and 4.09 x 10-1 %K-1 at 760 K. Therefore, we believe that the fabricated YAG: Yb3+/Nd3+ fluorescent materials have favorable application potential for optical thermometer.